拉萨地体锆石Hf同位素填图:对地壳性质和成矿潜力的约束

Mapping the Lhasa Terrane through zircon Hf isotopes: Constraints on the nature of the crust and metallogenic potential

迄今对拉萨地体（尤其是北部拉萨地体）地壳性质的空间展布特征并未得到有效讨论，直接限制了对拉萨地体成矿规律和成矿潜力的总结和评价。本文收集了拉萨地体已经发表和本团队未发表的中生代-早新生代（210～40Ma）大量酸性岩浆岩的锆石Hf同位素数据，利用Surferl0软件填制了拉萨地体锆石Ⅲ同位素和地壳模式年龄图。本文结果进一步证实中部拉萨地体曾经是一个微陆块，南部和北部拉萨地体总体显示新生地壳特征，在北部拉萨地体日土-盐湖一带，锆石εH（t）值和地壳模式年龄与南部拉萨地体的日喀则-八一一带类似，均以高的锆石εHt（t）值（因而非常明显的新生地壳）为特征。本文大量数据结合已有研究结果，表明地壳性质（新生地壳或古老成熟地壳）很可能是控制成矿作用类型的关键因素。通过与南部拉萨地体地壳性质和成矿作用类型的类比，结合北部拉萨地体目前已有矿床资料，提出日土-盐湖一带可能是北部拉萨地体最有潜力的Cu—Au成矿地带。

The spatial distribution of the nature of the crust beneath the Lhasa Terrane （ especially the northern Lhasa subterrane） remains poorly known so far, directly limiting the further summary and assessment on the metallogenic regularity and metallogenic potential of the Lhasa Terrane. This paper collects a large amount of zircon U-Pb age and Hf isotope data （ including published data in the literature and our abundant unpublished data） of silicic magmatic rock aged from Mesozoic to early Cenozoic （210 ~40Ma） to map the Lhasa Terrane using Surfer 10 software in terms of zircon Hf isotopes and crustal model ages. The results of this paper further confirm that （1） the central Lhasa subterrane was once a microcontinent, （2） the southern and northern Lhasa subterranes are dominated by the presence of juvenile crust, and （3） the zircon enf（t） and crustal model ages of silicie rocks from Rutog-Yanhu in the northern Lhasa subterrane are comparable to those of silieic rocks from Xigaze-Bayi in the southern Lhasa subterrane, both of which display high and positive zircon enf（t） （thus are undoubtedly of juvenile crust）. Abundant data summarized in this paper, together with the results previously obtained, indicate that the nature of the crust （juvenile or ancient） is most likely to be the critical factor to control types of mineralization. Considering the similarities of the nature of the crust and the types of mineralization between the northern and the southern Lhasa subterranes, in combination with the data currently available for the deposits in the northern Lhasa subterrane, this paper proposes that the Rutog-Yanhu area in the northern Lhasa subterrane has the greatest potential for the Cu-Au mineralization.